Base constructor for the class. It just returns a completely empty message object, which you'll need to populate with the various set_() methods, or use the read() method to read a Lost message from a file (followed by a call to from_asn() to turn the read's returned hash into a proper Lost message.

The constructor also initializes the Convert::ASN1 if it hasn't been initialized.

Sets the message's transaction-id.
Expects a valid Biblio::ILL::ISO::TransactionId.
my $tid = new Biblio::ILL::ISO::TransactionId("PLS","001","",
new Biblio::ILL::ISO::SystemId("MWPL"));
$msg->set_transaction_id($tid);
This is a mandatory field.